Elsevier

Agricultural Water Management

Volume 96, Issue 11, November 2009, Pages 1502-1508
Agricultural Water Management

Runoff water harvesting for dry spell mitigation for cowpea in the savannah belt of Nigeria

https://doi.org/10.1016/j.agwat.2009.06.005Get rights and content

Abstract

Cowpea yields obtained by smallholder farmers in the savannah belt of Nigeria are often less than the maximum obtainable yields because water deficit during critical growth stages is a common occurrence. Runoff harvesting to supplement direct rainfall may prove beneficial in improving current smallholder farming systems in this region. We study the effects of macro- and micro-catchments runoff harvesting, with or without in situ soil conservation, on cowpea yield in the savannah belt of Nigeria. The macro-catchments runoff harvesting (RH) experiment consisted of four treatments: conventional tillage and RH (CRH), zero tillage with RH (ZRH), reduced tillage with RH (RRH) and the direct rain fed (DR) treatment which served as the control in a randomized block design with four replicates. The micro-catchment experiment consisted of four treatments: runoff harvesting (RH), semi-circular bunds (SC), semi-circular bunds with runoff harvesting (SRH) and also direct rainfed (DR) in a randomized block design with four replicates. Results suggest that runoff harvesting can be used with existing conservation techniques. Applying harvested runoff water through supplemental irrigation provides the twin benefits of alleviating the prevailing slack periods and improving the yields of smallholder farming systems.

Introduction

Smallholder farmers in the savannah belt of Nigeria often experience low yields and sometimes crop failure in the second (late) cropping season. This is because rainfall is erratic, of high intensity and short duration, leading to large volumes of runoff and short dry spells during the growing season (Bello, 1997). Furthermore, the terrain is generally undulating with slopes ranging from 2% to 6%, such that erosion and soil loss are notable problems in the region. A dry spell refers to a period greater than 5 days without rainfall, which results in soil water deficit that could lead to crop-water stress (Barron et al., 2003).

Presently, the farmers adopt indigenous soil and water conservation techniques (in situ) such as mulching, conservation tillage and the use of circular and semi-circular bunds to combat these problems (Junge et al., 2007). Mulching entails the use of plant residue as surface cover to provide protection against rain-splash and preserve soil micro-climate by reducing evaporation. Circular or semi-circular bunds are usually low ridges of earth along the contour, which contain irrigation water or intercept runoff. Conservation tillage is often a form of non-inverting tillage action that retains protective amounts of residue mulch on the surface. Although in situ water conservation has a positive effect on soil-water availability, it has proven insufficient for bridging intra-seasonal dry spells of more than 5 days due to the high evaporation rate in the area (Barron et al., 2003). Cowpea is the main source of plant protein in the local diet and one of the major crops planted during the late planting season in Nigeria.

Runoff harvesting for agricultural production has been shown to reduce risk and increase crop yields in many countries of sub-Saharan Africa (Boers et al., 1986, Bruins et al., 1986, Fox and Rockström, 2003, Hatibu et al., 2003, Motsi et al., 2004, Barron and Okwach, 2005, Liu et al., 2005). The practice generates an alternative source of water where irrigation water is not readily available. Runoff harvesting may be categorized either as macro or micro depending on the distance between the runoff generating and receiving areas. In the micro runoff harvesting system, water is collected in an upland area and released into the area immediately below it. In the macro-system, the water is harvested from an area at an appreciable distance from where it is to be used. Sometimes, an intermediate storage outside the catchment basin is employed from where water is later used as supplemental irrigation. This is often referred to as water harvesting with supplemental irrigation (Tian et al., 2003).

Though rainwater harvesting for domestic use is common in Nigeria, the harvesting of runoff for crop production is relatively new. We compare micro- and macro-catchment (with storage) systems for dry spell mitigation of cowpea cultivation to determine the most effective system for improving smallholder farmers’ income and food security.

Section snippets

Location and climate

Our study was conducted in Afikuyomi village near Iwo town in the Iwo Local Government area of Osun State, Nigeria. The agro-ecological zone of the area (Fig. 1) is classified as grass savannah (Ashaye et al., 1998). The zone is dominated by smallholder farms that are smaller than 2 ha, on which cowpeas are intercropped with cassava and okra. Most farmers in the district practice in situ water harvesting using semi-circular bunds or mulching. The site lies at an altitude of 600 m above sea level.

Rainfall pattern and supplemental irrigation

The total rainfall for the late season was 256 mm while the estimated actual crop evapotranspiration was 340 mm. Thus the total rainfall was less than the actual water use, indicating water deficit. Furthermore, not all the rainfall would have been available to the crop as the runoff rate is very high in the study area due to high intensity (100–150 mm/h) of the rainfall. An estimated 25% of the rainfall becomes runoff (Fasinmirin and Olufayo, 2007). There were dry spells between 0 and 14, 15 and

Conclusions and recommendation

Current in situ water conservation using semi-circular bunds is preferable to micro-catchment runoff water harvesting in the study area. However, harvesting runoff water and storing it in an earthen pond is a viable method of supplementing crop water demand. An important step toward tapping the potential of this system is to channel a greater percentage of available runoff over the land to supplement soil moisture more efficiently (Hatibu et al., 2003). From a catchment water management

Acknowledgements

The authors are grateful to the UK Department for International Development (DFID) for funding this project under the “Needs assessment and uptake promotion of rainwater harvesting research in Nigeria” – Project No. R8390 for the benefit of developing countries. We are equally grateful to the staff of the Osun State Agricultural Development Project (OSSADEP) for the invaluable advice and assistance given during the field work.

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